Correlation kinetic energy of many-electron systems: a modified Colle-Salvetti approach

The Colle and Salvetti approach [Theoret. Chim. Acta, 37, 329 (1975)] to the calculation of the correlation energy of a system is modified in order to explicitly include into the theory the kinetic contribution to the correlation energy. This is achieved by deducing from a many electrons wave function, including the correlation effects via a Jastrow factor, an approximate expression of the one-electron reduced density matrix. Applying the latter to the homogeneous electron gas, an analytic expression of the correlation kinetic energy is derived. The total correlation energy of such a system is then deduced from its kinetic contribution inverting a standard procedure. At variance of the original Colle-Salvetti theory, the parameters entering in both the kinetic correlation and the total correlation energies are determined analytically, leading to a satisfactory agreement with the results of Perdew and Wang [Phys. Rev. B 45, 13244 (1992)]. The resulting (parameter-free) expressions give rise to a modified-local-density approximation that can be used in self-consistent density-functional calculations. We have performed such calculations for a large set of atoms and ions and we have found results for the correlation energies and for the ionization potentials which improve those of the standard local-density approximation.Comment: 26 page

Giovanni Sartori e la democrazia della Seconda Repubblica

Il saggio ripercorre e analizza criticamente tutti i passaggi istituzionali della cosiddetta Seconda Repubblica, ossia della peculiare democrazia maggioritaria che si imposta in Italia a partire dal 1994. Tali passaggi sono visti all'interno del pensiero di Giovanni Sartori e in particolare della sua teoria della democrazia. Tale pensiero si è manifestato sia attraverso opere scientifiche sia attraverso una continua attività pubblicistica, in particolare dalle colonne, come editorialista, del Corriere della Sera. Dall'esame di questo pensiero emerge una serrata e continua critica dei caratteri istituzionali della peculiare democrazia maggioritaria all'italiana.The essay traces and critically analyzes all the institutional steps of the so-called Italian Second Republic, that is the peculiar majoritarian democracy that is set in Italy since 1994. These steps are seen within the thoughts of Giovanni Sartori and in particular of his theory of democracy . Such thinking has manifested both through scientific works both through continuous publications, in particular from the columns, as a columnist, of the Corriere della Sera. From an examination of this thinking emerges a close and continuous criticism of the institutional character of the distinctive Italian style majoritarian democracy

Global hybrids from the semiclassical atom theory satisfying the local density linear response

We propose global hybrid approximations of the exchange-correlation (XC) energy functional which reproduce well the modified fourth-order gradient expansion of the exchange energy in the semiclassical limit of many-electron neutral atoms and recover the full local density approximation (LDA) linear response. These XC functionals represent the hybrid versions of the APBE functional [Phys. Rev. Lett. 106, 186406, (2011)] yet employing an additional correlation functional which uses the localization concept of the correlation energy density to improve the compatibility with the Hartree-Fock exchange as well as the coupling-constant-resolved XC potential energy. Broad energetical and structural testings, including thermochemistry and geometry, transition metal complexes, non-covalent interactions, gold clusters and small gold-molecule interfaces, as well as an analysis of the hybrid parameters, show that our construction is quite robust. In particular, our testing shows that the resulting hybrid, including 20\% of Hartree-Fock exchange and named hAPBE, performs remarkably well for a broad palette of systems and properties, being generally better than popular hybrids (PBE0 and B3LYP). Semi-empirical dispersion corrections are also provided.Comment: 12 pages, 4 figure

Hydrogen bond symmetrization and elastic constants under pressure of δ -AlOOH

International audienceThe elastic constants of δ-AlOOH have been calculated for applied pressures in the range 0–40 GPa using three exchange-correlation functionals, i.e. PBEsol, TCAsol and PBE. PBEsol and TCAsol, which describe the geometry of this system very well, give similar results, while the PBE values are smaller, a consequence of the fact that the PBE lattice parameters are too large. In agreement with the experiments, the calculations show that at low pressure the axial compressibility is greater in the b direction and smaller in the c direction, while the opposite is true at high pressure. This change takes place 5 GPa before the calculated hydrogen bond symmetrization transition. Combining this result with those reported in the experimental papers, one obtains a strong indication that symmetrization takes place at about 15 GPa, in excellent agreement with the PBEsol and TCAsol predictions

Can Standard DFT calculations correctly describe the physical properties of AIOOH under pressure?

International audienc

SS Luca e Martina

View of the drum and dome; SS Luca e Martina (the church of the painter's guild Accademia di S Luca in Rome) is planned as a Greek cross with apsidal endings and a dome over the crossing, set on a drum. The internal wall surface is vigorously articulated with pilasters and paired free-standing columns recessed under a continuous entablature, recalling Michelangelo's usage at the Biblioteca Laurenziana in Florence. The lower storey of the façade is structured in the same way, with engaged columns and projecting pilasters. In both storeys of the façade the wall describes a gentle convex curve between the central bay and the coupled pilasters at the sides: thus a main theme of Baroque church façade design appeared in Rome. Source: Grove Art Online; http://www.groveart.com/ (accessed 11/5/2007

Le dimensioni territoriali della politica. Lo Stato tra frammentazione nazionale e integrazione regionale

Il capitolo tratta dei rapporti tra la politica e la sua (variabile nel tempo) dimensione territoriale. Oggi la principale dimensione territoriale della politica è ancora rappresentata dallo stato, che è tuttavia sfidato dal basso (nazionalismi, regionalismi, localismi) e dall'alto (integrazioni regionali come l'Ue, globalizzazione, ecc.)

Come gli Stati diventano democratici

Il volume analizza i processi di democratizzazione, divenuti uno dei fenomeni più interessanti dal punto di vista comparato degli ultimi cinquanta anni. Una volta analizzati i caratteri definitori dei regimi democratici e delle varietà dei regimi non democratici, il volume tratta delle fasi della democratizzazione, delle condizioni interne e internazionali che favoriscono o ostacolano lo sviluppo della democrazia e degli esiti delle democratizzazioni (quali tipi di democrazia emergono e quali problemi presentano. L'ultimo capitolo è dedicato alle prospettive di sviluppo della democrazia oltre e al di sopra degli Stati e dei possibili problemi